The concept of user equipment (UE) reachability is described in 3GPP TS 23.501 v0.3.0 clauses 5.40.1 (CM-IDLE) and 5.4.2 (CM-CONNECTED). In short, reachability management is responsible for detecting whether the UE is reachable and providing UE location (i.e., access node) for the network to reach the UE. This is done by paging UE and UE location tracking. The UE location tracking includes both UE registration area tracking (i.e., UE registration area update) and UE reachability tracking (i.e., UE periodic registration area update). Such functionalities can be either located at 5GC (in case of CM-IDLE state) or 5G-RAN (in case of CM-CONNECTED state).